Here's an interesting circuit to monitor the supply of three-phase circuits. The circuit shown in figure 1 allows to verify the sequence of the phases of a three-phase system.
When the neon lamp in phase C is on, the sequence is correct. When the phase A neon lamp is on, then the phase sequence is incorrect. The switch allows to select when the circuit operates with a source of 230 V. In the normal condition, the circuit operates with sources of 480 V.
In figure 2 we have the assembly of this solution on a printed circuit board.
MATERIAL LIST
NE-1, NE-2 - Standard neon lamps
C1 - 47 nF x 400 V - polyester capacitor
R1, R2, R3, R4 - 39 k ohms x ½ W - resistors
S1 - 2-pole x 2 positions switch
Several:
Printed circuit board, test claws, mounting box, wires, solder, et
